(1) Field of the Invention
This invention relates to a webbing-locking mechanism suitable for use in a vehicle seat belt.
(2) Description of the Prior Art
In order to effectively restrain each vehicle occupant in the event of emergency such as vehicle collision or the like, a variety of improvements have been made to various devices, mechanisms or systems used in seat belts. In the field of retractors which are adapted to take up webbings fastened on vehicle occupants, a wide variety of proposals have been made to directly clamp each webbing at the outlet side of its corresponding retractor so as to minimize the length of the webbing which may be pulled out of the retractor in the event of emergency, for example, to firmly hold the webbing between a guide roller allowing the webbing to extend over a predetermined length of its circumference and a clamp member fixedly provided on a base.
In prior art webbing-locking mechanisms of the above-mentioned sort, each webbing-locking mechanism is so constructed that rotation of its guide roller is stopped directly by a pawl. Accordingly, such conventional webbing-locking mechanisms involve a danger that vehicle occupants may not be fully protected because their pawls may be struck back by their corresponding guide rollers or may slide on their corresponding guide rollers, thereby failing to stop the guide rollers surely and thus allowing their respective webbings to be pulled out of the retractors over such lengths as correspond to their tightened lengths in the retractors and allowing the webbings to slippingly pass between the guide rollers and their matching clamp members.
It seems to be effective to stop rotation of each guide roller in two or more steps in order to overcome such drawbacks of the prior art webbing-locking mechanism. An example of a guide roller equipped with a two-step locking mechanism is seen in U.S. Pat. No. 4,249,708 issued Feb. 10, 1981 to Shuichi Asano, especially, in FIGS. 12-14 of the Asano patent. A movement of a transmission lever causes an auxiliary pawl to engage with its corresponding auxiliary gear. However, this locking mechanism requires the transmission lever and a heavy pendulum as impact sensing means in order to activate the first and second pawl surely via the transmission lever. Coupled with the long drive-force transmission path from the pendulum, the above mechanism is accompanied by drawbacks that the locking mechanism is unavoidably large and complex as a whole.